ATCA survey of water masers in the Large Magellanic Cloud

We have analysed archival data taken with the Australia Telescope Compact Array (ATCA) during 2001--2003 and detected nine new interstellar and circumstellar water masers in the LMC. This takes the total number of star formation water masers in the LMC to 23, spread over 14 different star forming regions and three evolved stars. Three water maser sources (N105a/MC23, N113/MC24, N157a/MC74) have been detected in all the previous observations that targeted these sites, although all show significant variability on timescales of decades. The total number of independent water maser sources now known in the LMC means that through very long baseline interferometry astrometric measurements it will be possible to construct a more precise model of the galactic rotation of the LMC and its orbital motion around the Milky Way Galaxy.

First detection of CO lines in a water fountain star

[Context] Water fountain stars are very young post-AGB stars with high velocity water maser jets. They are the best objects to study the onset of bipolar jets from evolved stars due to their young dynamical ages. [Methods] We use the Arizona Radio Observatory 10m telescope to observe the CO J=2-1 line and compare the line parameters with that of masers. [Results] We report the detection of 12CO and 13COJ=2-1 lines from IRAS 16342-3814. The inferred 12CO mass loss rate is an order of magnitude lower than the infrared and OH mass loss rates, indicating a very cold and thick O-rich circumstellar envelope around the star. We also find a 12CO expansion velocity of Vexp = 46 +- 1 km/s that is too high for an AGB wind and confirm the systemic velocity of 44 +- 1 km/s. In addition we measure a very low 12CO/13CO line ratio of 1.7. [Conclusions] The first detection of CO lines has provided a new way to investigate the water fountain stars. Given the high expansion velocity of the CO gas and its relation to maser velocities, we infer that the CO emission region is co-located with the OH mainline masers in the warm base of the optical bipolar lobes, while the high velocity OH1612MHz and H2O masers are located in the side walls and at the farthest ends of the bipolar lobes, respectively. Further observations are highly desired to understand the very low 12CO/13CO line ratio.